The present invention relates to thin film inductors (see definition of “thin film inductor,” below) and more particularly to thin film inductors having ferromagnetic yokes (sometimes herein referred to as “yoke portions” or “pole portions”).
The integration of inductive power converters onto silicon, by using fabrication techniques developed for integrated circuits, has reduced the cost, weight, and size of electronics devices. For example, one challenge to developing a fully integrated “on silicon” power converter is the development of high quality thin film inductors. To be viable, the inductors should have a high Q, a large inductance per unit volume and per unit of footprint area, have low energy losses (also called high energy efficiency) and a large energy storage per unit area.
Thin film magnetic inductors typically include: (i) a ferromagnetic bottom yoke portion formed as a thin film layer laid on top of a base portion (for example, a silicon substrate layer); (ii) a ferromagnetic top yoke portion formed as a thin film layer; (iii) magnetic via zones, which are paths of low magnetic reluctance between the bottom pole portion and top pole portion (see definition of “magnetic via zone,” below for a more precise definition); and (iv) a current carrier portion (for example, a portion of a spiral winding or a stripline conductor) that passes between the top and bottom yoke portions with respect to the vertical direction and between the via zones with respect to the horizontal direction. The low reluctance paths of the via zones may be formed by: (i) shaping the top and bottom pole pieces so they come into contact (or at least close proximity) in the via zones; or (ii) providing dedicated via portions, made of magnetically permeable material) that serve as a bridge for magnetic flux between the top and bottom yoke portions.